Fix

assets/sw.js

@@ -213,6 +213,19 @@ async function answer(input, event) {
   }
 }
 
+// Pages are always asked for with revalidation forced.
+//
+// server.py marks them no-cache, which asks the browser for the same thing --
+// but this worker's own fetch goes through the browser's HTTP cache too, so a
+// page stored under an earlier and wronger Cache-Control keeps being served
+// from it until that entry expires, however many times the library version
+// changes underneath. Saying it on the request is what gets past one that
+// already is. Costs a conditional GET, which the response header was asking
+// for anyway.
+function pageRequest(url) {
+  return new Request(url, { cache: 'no-cache' });
+}
+
 async function readText(input, event) {
   const res = await answer(input, event);
   if (!res || !res.ok) throw new Error('cannot load ' + (input.url || input));
@@ -250,7 +263,7 @@ const MISSING_NOTICE = ['Not found', 'There is no page at this address.'];
 async function fragmentFor(path, event) {
   let res;
   try {
-    res = await answer(path, event);
+    res = await answer(pageRequest(path), event);
   } catch (err) {
     return view.notice(...OFFLINE_NOTICE);
   }
@@ -335,7 +348,7 @@ async function fillLibrary() {
     while (missing.length && !stopped) {
       const url = missing.pop();
       try {
-        const res = await fromNetwork(new Request(url), DOWNLOAD_TIMEOUT_MS);
+        const res = await fromNetwork(pageRequest(url), DOWNLOAD_TIMEOUT_MS);
         // A response that arrived but is not usable -- a page that has since
         // been removed, say -- is skipped rather than retried. The connection
         // is plainly fine, and stopping for it would strand everything after.